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Siegfried, MR, Fricker HA.  2018.  Thirteen years of subglacial lake activity in Antarctica from multi-mission satellite altimetry. Annals of Glaciology. 59:42-55.   10.1017/aog.2017.36   AbstractWebsite

The ability to detect the surface expression of moving water beneath the Antarctic ice sheet by satellite has revealed a dynamic basal environment, with implications for regional ice dynamics, grounding-line stability, and fluxes of freshwater and nutrients to the Southern Ocean. Knowledge of subglacial activity on timescales important for near-term prediction of ice-sheet fluctuations (decadal to century) is limited by the short observational record of NASA's Ice, Cloud, and land Elevation Satellite (ICESat) laser altimetry mission used to generate the last continent-wide survey (2003-08). Here, we use synthetic aperture radar-interferometric-mode data from ESA's CryoSat-2 radar altimetry mission (2010-present), which samples 45 of the ICESat-derived subglacial lakes, to extend their time series to the end of 2016. The extended time series show that there have been surface-height changes at 20 of the 45 lakes since 2008, indicating that some of these features are persistent and potentially cyclic, while other features show negligible changes, suggesting these may be transient or nonhydrological features. Continued monitoring of active lakes for both height and velocity changes, as well as developing methods for identifying additional lakes, is critical to quantifying the full distribution of active subglacial lakes in Antarctica.

Fricker, HA, Padman L.  2012.  Thirty years of elevation change on Antarctic Peninsula ice shelves from multimission satellite radar altimetry. Journal of Geophysical Research-Oceans. 117   10.1029/2011jc007126   AbstractWebsite

We use data acquired between 1978 and 2008 by four satellite radar altimeter missions (Seasat, ERS-1, ERS-2 and Envisat) to determine multidecadal elevation change rates (dh(i)/dt) for six major Antarctic Peninsula (AP) ice shelves. In areas covered by the Seasat orbit (to 72.16 degrees S), regional-averaged 30-year trends were negative (surface lowering), with rates between -0.03 and -0.16 m a(-1). Surface lowering preceded the start of near-continuous radar altimeter operations that began with ERS-1 in 1992. The average rate of lowering for the first 14 years of the period was typically smaller than the 30-year average; the exception was the southern Wilkins Ice Shelf, which experienced negligible lowering between 2000 and 2008, when a series of large calving events began. Analyses of the continuous ERS/Envisat time series (to 81.5 degrees) for 1992-2008 reveal a period of strong negative dhi/dt on most ice shelves between 1992 and 1995. Based on prior studies of regional atmospheric and oceanic conditions, we hypothesize that the observed elevation changes on Larsen C Ice Shelf are driven primarily by firn compaction while the western AP ice shelves are responding to changes in both surface mass balance and basal melt rates. Our time series also show that large changes in dh(i)/dt can occur on interannual time scales, reinforcing the importance of long time series altimetry to separate long-term trends associated with climate change from interannual to interdecadal natural variability.

Fricker, HA, Padman L.  2002.  Tides on Filchner-Ronne Ice Shelf from ERS radar altimetry. Geophysical Research Letters. 29   10.1029/2001gl014175   AbstractWebsite

[1] We use harmonic analysis of 8 years of ERS satellite radar altimeter (RA) data at orbital crossovers to retrieve complex amplitude (amplitude and phase) coefficients for several major tidal harmonics over the Filchner-Ronne Ice Shelf (FRIS), Antarctica. We describe a method for estimating the accuracy of this method, which ranges from similar to2 to 8 cm per harmonic. A comparison between M-2 complex amplitude from a recent ocean model and from our ERS RA analyses identifies two regions of the FRIS where the RA data are inconsistent with the model. In both regions the differences can be attributed to incorrect specification of the grounding line location in the model. Our study demonstrates the value of ERS RA data in Antarctic ice shelf tide modeling, and the potential for future altimeter satellites with high polar orbits to contribute to the definition of global tide height variations.

Padman, L, Fricker HA.  2005.  Tides on the Ross Ice Shelf observed with ICESat. Geophysical Research Letters. 32   10.1029/2005gl023214   AbstractWebsite

The Ice, Cloud and land Elevation Satellite (ICESat) provides the first opportunity for measurement of surface elevation h(i) over the portions of the Antarctic ice shelves that are south of the European Remote Sensing (ERS) satellite maximum latitude (81.5 degrees S). The dominant source of short-period variability in h(i) is ocean tides. We use crossover elevation difference (Delta h(i)) data from the Ross Ice Shelf (RIS) to demonstrate ICESat's ability to detect the tidal signal, and to compare the accuracy of several tide models. The root-mean-square (rms) value of all RIS measurements of Delta h(i) is approximate to 0.74 m; after removing the tide using the most accurate model, the rms of the residual signal in regions of optimal model performance is approximate to 0.16 +/- 0.03 m. This value corresponds to an uncertainty in h(i) of 0.11 +/- 0.02 m. We postulate that the primary sources of the residual signal are tide model errors and the inverse barometer effect.

Borsa, AA, Fricker HA, Bills BG, Minster JB, Carabajal CC, Quinn KJ.  2007.  Topography of the salar de Uyuni, Bolivia from kinematic GPS. Geophysical Journal International. 172:31-40.   10.1111/j.1365-246X.2007.03604.x   AbstractWebsite

The salar de Uyuni in the Bolivian Andes is the largest salt flat on Earth, exhibiting less than 1 m of vertical relief over an area of 9000 km(2). We report on a kinematic Global Positioning System (GPS) survey of a 45-by-54 km area in the eastern salar, conducted in September 2002 to provide ground truth for the Ice Cloud and land Elevation Satellite (ICESat) mission. GPS post-processing included corrections for long-period GPS noise that significantly improved survey accuracy. We fit corrected GPS trajectories with 2-D Fourier basis functions, from which we created a digital elevation model (DEM) of the surface whose absolute accuracy we estimate to be at least 2.2 cm RMSE. With over two magnitudes better vertical resolution than the Shuttle Radar Topography Mission data, this DEM reveals decimetre-level topography that is completely absent in other topographic data sets. Longer wavelengths in the DEM correlate well with mapped gravity, suggesting a connection between broad-scale salar topography and the geoid similar to that seen over the oceans.

Phillips, HA, Laxon SW.  1995.  Tracking of Antarctic Tabular Icebergs Using Passive Microwave Radiometry. International Journal of Remote Sensing. 16:399-405. AbstractWebsite

Passive microwave images of Antarctica from the Special Sensor Microwave Imager (SSM/I) are used to track two giant tabular icebergs that originated from the Larsen ice shelf in 1986. Since microwave radiation is relatively insensitive to weather and unaffected by lighting conditions, the SSM/I instrument provides all-weather, year-round viewing. The icebergs are visible almost every day giving an ideal temporal resolution for tracking their motion. One of the icebergs was tracked until October 1988, six months after its last position noted in the Navy/NOAA Joint Ice Centre ice charts. The tracks of both icebergs reveal motion in sympathy with observed oceanographic currents and eddies.

MacAyeal, DR, Okal EA, Aster RC, Bassis JN, Brunt KM, Cathles LM, Drucker R, Fricker HA, Kim YJ, Martin S, Okal MH, Sergienko OV, Sponsler MP, Thom JE.  2006.  Transoceanic wave propagation links iceberg calving margins of Antarctica with storms in tropics and Northern Hemisphere. Geophysical Research Letters. 33   10.1029/2006gl027235   AbstractWebsite

We deployed seismometers on the Ross Ice Shelf and on various icebergs adrift in the Ross Sea ( including B15A, a large 100 km by 30 km fragment of B15, which calved from the Ross Ice Shelf in March, 2000). The data reveal that the dominant energy of these floating ice masses is in the 0.01 to 0.1 Hz band, and is associated with sea swell generated in the tropical and extra-tropical Pacific Ocean. In one example, a strong storm in the Gulf of Alaska on 21 October 2005, approximately 13,500 km from the Ross Sea, generated swell that arrived at B15A immediately prior to, and during, its break-up off Cape Adare on 27 October 2005. If sea swell influences iceberg calving and break-up, a teleconnection exists between the Antarctic ice sheet mass balance and weather systems worldwide.

Shepherd, A, Fricker HA, Farrell SL.  2018.  Trends and connections across the Antarctic cryosphere. Nature. 558:223-232.   10.1038/s41586-018-0171-6   AbstractWebsite

Satellite observations have transformed our understanding of the Antarctic cryosphere. The continent holds the vast majority of Earth's fresh water, and blankets swathes of the Southern Hemisphere in ice. Reductions in the thickness and extent of floating ice shelves have disturbed inland ice, triggering retreat, acceleration and draw-down of marine-terminating glaciers. The waxing and waning of Antarctic sea ice is one of Earth's greatest seasonal habitat changes, and although the maximum extent of the sea ice has increased modestly since the 1970s, inter-annual variability is high, and there is evidence of longer-term decline in its extent.